Fix flaky test CacheStatsAPIIndicesRequestCacheIT.testNullLevels()

[peteralfonsi]

Description

I introduced CacheStatsAPIIndicesRequestCacheIT in this recent PR but I have found it to be flaky (example here). I created an issue for this here.

If levels is uninitialized in CommonStatsFlags, the String[] levels passed into DefaultCacheStatsHolder is usually an empty list. This is the expected behavior. But in some cases, DefaultCacheStatsHolder receives null instead of an empty list, and in this case, the XContent output derived from it has unexpected fields. To fix this we add an explicit null check when DefaultCacheStatsHolder constructs the object which produces XContent, and use an empty list if null is passed in.

We also initialize CommonStatsFlags.levels to be an empty String[] rather than null, as I found not doing this can rarely cause RestNodesStatsActionTests.testUnrecognizedMetric() to flake for the same reason.

Finally, fixes inconsistency with how null levels were used in tests.

Related Issues

Resolves #13458

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Failing checks are inspected and point to the corresponding known issue(s) (See: Troubleshooting Failing Builds)
• Commits are signed per the DCO using --signoff
• Commit changes are listed out in CHANGELOG.md file (See: Changelog)
• Public documentation issue/PR created

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[github-actions]

❌ Gradle check result for 8b837aa: FAILURE

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[github-actions]

❌ Gradle check result for 79331c4: FAILURE

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[github-actions]

❌ Gradle check result for 917cf0c: FAILURE

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[github-actions]

❌ Gradle check result for 2609cf7: FAILURE

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[dblock]

❌ Gradle check result for 2609cf7: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

58 failures ugh

[peteralfonsi]

Yeah, I think the BWC tests fail because this PR which touches related code, bumping versions from 3.0.0 to 2.14.0 to match what's present in the 2.x branch, hadn't been merged into this branch yet. Merging main into this branch should fix it I hope?

[github-actions]

❌ Gradle check result for 2609cf7: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for ec252f5: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[peteralfonsi]

BWC tests no longer fail but seeing failure for RemoteReplicaRecoveryIT.testReplicaRecovery. I don't see a flaky test issue for this test, but I don't think this change could have caused it to fail as it only affects new code. The test also runs fine on my end.

[dblock]

BWC tests no longer fail but seeing failure for RemoteReplicaRecoveryIT.testReplicaRecovery. I don't see a flaky test issue for this test, but I don't think this change could have caused it to fail as it only affects new code. The test also runs fine on my end.

@peteralfonsi open a new flaky test issue please?

[peteralfonsi]

#13473

[github-actions]

✅ Gradle check result for 27b9614: SUCCESS

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.37%. Comparing base (b15cb0c) to head (27b9614).
Report is 245 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #13457      +/-   ##
============================================
- Coverage     71.42%   71.37%   -0.05%     
- Complexity    59978    60950     +972     
============================================
  Files          4985     5050      +65     
  Lines        282275   286804    +4529     
  Branches      40946    41550     +604     
============================================
+ Hits         201603   204719    +3116     
- Misses        63999    65170    +1171     
- Partials      16673    16915     +242     

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